Thinking about coconuts
When I was a child I used to go on a long car journey with my father to visit my grandparents in the North of England. Apparently my father would complain to my mother that the journeys were exhausting, because he had to respond to a constant barrage of strange questions from his inquisitive son. My own son, the youngest, is now like I was then, and constantly asks difficult, and sometimes bizarre, questions. I do my best to answer his questions as well as I can, and if I doubt my answer, or do not know the answer, I will research it and then explain it to him.
Yesterday one of the things on his enquiring mind was the coconut. Why are they so big? Why do they have water in them? Are they a nut or a fruit? What is the white stuff for? Did dinosaurs eat coconuts?
I remember having a similar interest in coconuts at his age. In fact, one of my high-school memories is related to coconuts. Biology was my favorite subject at school, and I had a great biology teacher called Dr Collins, who was both a great teacher and good fun. I did very well in that subject and would have been top of the class if it wasn’t for my childhood rival, an extremely studious and clever boy called Daniel.
One time Dr Collins gave us homework to create a presentation about any subject in biology that we found interesting, and the next lesson he asked some of us to give our presentations in front of the class. Daniel was first up. He gave a very long talk about moths and butterflies. Annoyingly he referred to them as Lepidoptera, and only used the latin names of the species he talked about, rather than the nicer common names. Vanessa cardui rather than Painted Lady, Vanessa atalanta rather than Red Admiral. It was extremely boring and annoying. Like Daniel himself to my younger self. Dr Collins asked me to present next. I held up a picture of a Coconut crab:
I explained that this type of crab can climb coconut trees and knock down coconuts to eat, and asked “How did that evolve?”. There was a pause, and then Dr Collins asked “Is that it?” I said that it was, and Dr Collins laughed and said it was very interesting and thought-provoking.
I now have a degree in biology so should be able to answer coconut-related questions with some proficiency. I explained to my son that coconuts tend to grow on shorelines in the Pacific region, and that their unusual size and shape may be a distribution mechanism, the husk acting as a float. I hadn’t thought about the water inside them but speculated that, if a coconut is growing on a shoreline the young plant may need a small supply of fresh water until it can grow roots that are able to desalinate the salty water available on to it.
Over the years I’ve come to realize that things I thought I knew actually turned out to be incorrect upon further research, and so I did a bit of fact-checking. Surprisingly it seems that there is still debate amongst botanists as to whether the unusual form of the coconut is a distribution mechanism, or just there to stop the shell breaking when they fall onto potentially hard and rocky ground. Arguments against it being a distribution mechanism include that they don’t remain viable for very long in sea water, and their natural distribution isn’t as wide as you would expect if they could survive long journeys at sea. However, to my mind those things don’t eliminate the possibility that it is a distribution mechanism, just that it may not be a distribution mechanism over long distances. If a coconut falls into the sea and it washes up 100 meters further up the beach and germinates there, it is still a distribution mechanism and aids in the reproduction of the plant. As with many things in evolution, and indeed life in general, the answer isn’t one thing or the other, but a bit of both. The husk both protects the coconut when it falls, and it can act as a buoyancy aid if it falls in the sea so the seed is distributed a bit further up the coast from the parent plant.